grow box set up

i`am building a grow box that is 4`x4`x7` and plan on useing a 600 watt mh/hps light growing 6 lemon skunk plants... will the light be enough.if so i plan on growing them until they reach about 30`` in heigth then top and start budding,if i do this how much taller will these plants grow. i will grow in 4 gallon planter, someone said that i would run out of room if i waite until they are 30 inchs tall before switching to 12/12 budding... i thought that once you started budding that they would only get another 1&half feet taller that would make it a 4 foot plant and a foot for the planter thats five feet and will have another foot or so for light adjustment.is this true about how much more they will grow dureing budding or should i bud them before they are 30 inches please HELP!!!!... also if i`am right about size of plants then can someone tell me if my light will be enough and roughly how much will they produce each plant...

they will grow to 2 to 3 times their size. You still have to consider room for your light. Are you gonna grow in buckets on the floor or a flood table ?